Do not report addons with different cachekey but same version & adding summary to output

[step2yeung]

This PR fixes a bug and adds a new summary section to the output

1. Some addons may return a custom cachekey, in my example, the addon returns a different cachekey if an addon is declared from the root vs as child's dependent. ECAG(Ember-cli-addon-guard) reported that addon as a failure, when the version is actually the same. Fix was to have ECAG to also check for version.
2. Having a summary section on the top of the output helps with parsing all the information easily. eg:

Summary
Number of addons with multiple versions: 16

@embroider/macros: [0.36.0 , 0.24.1]
ember-get-config: [0.2.4 , 0.3.0]
ember-lifeline: [4.1.5 , 3.1.1 , 5.1.0 , 6.0.1]
ember-test-selectors: [5.0.0 , 3.0.0]
ember-batcher: [3.0.0 , 4.0.1]

Details
ember-cli-addon-guard determined that your application is dependent on multiple versions of the following run-time addons:

@embroider/macros
...